This invention pertains to control of the flow of solids onto or off a dry, inclined conveyor belt type solids separating system, which control increases the separating efficiency and surface area utilization of the conveyor belt. The separating system is for separating spherically-shaped rolling solids from irregularly-shaped nonrolling solids and is especially useful for oil shale retorting processes using spherically-shaped solid heat carriers which are recycled through the retorting process.
It is sometimes necessary to separate spherically-shaped rolling solids from irregularly-shaped nonrolling solids. This invention relates to apparatus and methods for carrying out such separation. The system of this invention is especially useful when a dry, high temperature, high capacity, confined system with controlled atmospheric emissions is required, for example, separating spherical solid heat carriers from spent shale in an oil shale retorting process. It is desirable that the separation efficiency be good while carry-over, loss, or attrition of the desired solids, e.g., heat carriers, is low. Yet, these objectives are difficult to achieve, especially when the two classes of solids have overlapping size ranges with relatively similar specific gravities or have overlapping particle weights. It is also desirable that the separating system be relatively compact and have relatively few moving parts in light of the mass of solids to be separated per unit time. A high capacity system with a high degree of adaptability to varying mass flow rates and solids mixtures is highly desired.
Copending Applications Ser. No. 749,505, filed Dec. 10, 1976, entitled "Separation and Recovery of Heat Carriers in an Oil Shale Retorting Process", and Ser. No. 749,504, filed Dec. 10, 1976, entitled "Double Inclined and Stacked Conveyor Belt Solids Separation System", which are owned by a common assignee and are incorporated herein, cover embodiments of a continuously restored inclined surface separating system, which embodiments are especially useful for separating spherical solid heat carriers from spent shale solids in an oil shale retorting process.
One of the embodiments of Application Ser. No. 749,505 covers a continuously restored, inclined conveyor belt solids separation system of the type provided herein. In a system of this type, a mixture of rolling solids and nonrolling solids is fed onto the upper surface of a moving conveyor belt inclined along its longitudinal axis. When the solids impact the surface of the belt, their momentum tends to cause them to initially move up or down the belt. Application Ser. No. 749,504 covers the vertical stacking of conveyor belt separators and a double inclined conveyor belt wherein the belt is inclined both sideways and upward in relation to its longitudinal axis. In this latter system, the momentum of the solids fed onto the belt is up an incline or inclines of the belt so that the solids initially move up an incline.
In both conveyor belt systems, the initial momentum of the solids decreases the effective separating surface area of the belt and tend to aggravate interaction between the solids which creates solids bridging or trapping problems where one type of solid is trapped by moving particles of the other type. This decreases the separation efficiency of the system and increases carry-over or loss of the desired solids.
In both systems, the surface of the inclined conveyor belt is continuously moved upward past the solids feed point and the irregularly-shaped, nonrolling solids move upwardly with the belt until they are removed from the belt either by falling off the end of the belt or until they are pushed off the belt. The spherically-shaped, rolling solids roll down either toward the end of the belt or toward the side of the belt until they are removed from the belt either by falling off the end or side of the belt or until they are pushed off the belt. In either case, when a group of solids has a relatively unimpeded path it may follow in leaving the belt or the group of solids is pushed off the belt in an uncontrolled manner, the group of solids will carry solids of the other class off the belt. Carryover decreases separation efficiency or increases loss of desirable solids, whichever the case may be.
This invention provides several improvements in the inclined conveyor belt system which increases utilization of the surface of an inclined conveyor belt separating system and increases separation efficiency while reducing carry-over or loss of the desired solids.